A method for preparing diesel

Abstract

This invention discloses a method for preparing diesel fuel, which involves mixing crude oil fractions from direct coal liquefaction with crude oil fractions from indirect coal liquefaction, followed by hydrogenation refining and separation to obtain diesel fuel. The preparation method is simple, and the diesel fuel produced has excellent properties.

Description

Technical Field

[0001] The present invention relates to the field of aviation fuel, and in particular to a method for preparing diesel. Specifically, the present invention is a method for producing diesel by using coal direct liquefaction crude oil fraction and coal indirect liquefaction crude oil fraction as raw materials and blending them in a certain proportion and then performing hydrogenation refining. Background Art

[0002] my country is rich in coal but short of oil, with coal accounting for 94% of fossil energy. For quite a long time, coal will remain the main energy source in my country, so how to use coal more efficiently and cleanly and ensure my country's energy security and national defense security is a major issue that needs to be solved urgently. According to the characteristics of my country's coal types and resources, direct coal liquefaction and indirect coal liquefaction are the two main development paths for coal-to-liquid products. The development of a complete set of coal-to-liquid products technology meets the major needs of my country's economic development, and at the same time has great strategic significance for improving the country's energy security capabilities, promoting the transformation of the modern coal industry, and helping to upgrade military special fuels and aerospace fuels.

[0003] The direct coal liquefaction process is a way to utilize coal by pyrolyzing and liquefying coal macromolecules under the action of solvents and catalysts under high temperature and high pressure hydrogen conditions to produce small molecular oil products. In the direct liquefaction reactor, the coal powder mainly undergoes macromolecular breakage and free radical hydrogenation reactions. The resulting liquefied primary products are mainly aromatics and cycloalkanes. Subsequently, the liquefied oil products enter the hydrogenation stabilization unit, and the heavy product part is used as solvent oil for circulating coal slurry, and the light part enters the hydrogenation reforming unit. After desulfurization, denitrogenation, aromatic saturation and partial cracking, the product obtained basically retains the molecular structure characteristics of coal. At the same time, the fuel components produced have the advantages of low sulfur and nitrogen content, high cycloalkanes content, high specific gravity, and low freezing point.

[0004] The coal indirect liquefaction process uses coal as raw material, which is first gasified to form synthesis gas (CO and H2). Then, under the action of a catalyst, the Fischer-Tropsch synthesis reaction generates crude products such as light oil, heavy oil and heavy wax. The liquefied petroleum gas is separated by steam stripping and then enters a refining reactor for hydrogenation refining. The refined products are fractionated into diesel, crude naphtha and heavy products. The crude naphtha is separated into liquefied petroleum gas and naphtha through adsorption desorption and stable distillation. The heavy products enter a vacuum tower for further separation. The bottom product of the tower is hydrocracking, and the other products are fractionated and cut into naphtha and diesel after hydrodecondensation.

[0005] The liquefied crude oil from the coal direct liquefaction unit has high aromatics, sulfur and nitrogen content. If it is used directly to prepare diesel, it has high requirements on the selected hydrogenation catalyst and corresponding process conditions, and the process is long and the conditions are harsh. In addition, the cetane number of the produced direct liquefied diesel is low and can only be used as a blending component for automotive diesel.

[0006] The carbon number of the indirect coal liquefaction product is high. In order to obtain the target product, it needs to go through hydrofining, cracking and isomerization process units, and the processing flow is relatively long. In addition, due to the low density and high condensation point of indirect liquefied diesel and the low octane number of gasoline components, the indirect liquefaction product can often only be used as blending oil and cannot be directly sold as finished oil.

[0007] Invention patent CN 101144032 A is a mixture of diesel fractions obtained by hydrofining direct coal liquefaction oil and diesel fractions obtained by indirect coal liquefaction. The properties of the diesel product obtained can meet the requirements of Euro III or Euro IV diesel standards. From the perspective of product characteristics, direct coal liquefaction and indirect coal liquefaction products have their own advantages and disadvantages. Although the problem that the two products cannot become qualified diesel has been solved by product blending, obtaining the two products still requires strict process conditions and lengthy process flows. If the processing of the crude products of the two processes is comprehensively considered and designed as a whole, it can play a positive role in maximizing the advantages of the properties of the two technical products, flexibly adjusting the product structure, reducing investment and production energy consumption, and shortening the process complexity. Summary of the invention

[0008] The present invention provides a method for preparing diesel to make up for the deficiencies of the prior art. The diesel is obtained by mixing a crude oil fraction directly liquefied from coal with a crude oil fraction indirectly liquefied from coal, and then hydrogenating and refining the mixture and separating the mixture. The preparation method is simple and the diesel has good indexes.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing diesel, the method comprising the following steps:

[0011] (1) dissolving coal in a solvent to prepare an oil-coal slurry and reacting it with hydrogen to directly liquefy the coal, and the generated coal direct liquefaction crude oil is separated in a first fractionation tower to obtain a first light distillate oil and a heavy distillate oil; the first light distillate oil enters an oil product mixer; optionally, the heavy distillate oil is used as a solvent raw material to perform solvent hydrogenation stabilization in a hydrogenation stabilization reactor;

[0012] (2) the coal gasification synthesis gas is subjected to a Fischer-Tropsch synthesis reaction, and the synthesized coal indirect liquefaction crude oil is separated in a second distillation tower to obtain a second light distillate oil and wax, and the second light distillate oil enters the oil product mixer;

[0013] (3) mixing the first light distillate oil and the second light distillate oil in a certain ratio, and then performing a hydrotreating reaction in a hydrotreating reactor;

[0014] (4) Separating the hydrogenation product obtained in step (3) to obtain a diesel product.

[0015] In step (1), the coal direct liquefaction reaction is well known in the art, and for details, reference may be made to the coal direct liquefaction method disclosed in CN 1598351A, which will not be described in detail herein; the coal direct liquefaction crude oil is liquefied crude oil obtained by a coal direct liquefaction process, for example, it can be obtained by removing light components and solid residues from the product oil leaving the coal direct liquefaction reactor, that is, no further hydroreforming or hydrofining is required, for example, its distillation range is usually within the range of 30 to 500°C.

[0016] In one embodiment, in step (1), the distillation temperature of the first distillation tower is 290-300°C, the fraction below the distillation temperature is taken as the first light distillate oil, and the remaining fractions are taken as heavy distillate oil.

[0017] In step (1) of the present invention, the heavy distillate oil is hydrogenated and stabilized to prepare a circulating solvent; in one embodiment, in step (1), when the hydrogenation stabilization reaction is carried out, the reaction temperature of the hydrogenation stabilization reactor can be 300-400°C, such as 340, 360 or 380°C, the reaction pressure can be 12.0-20.0MPa, such as 14, 16 or 18MPa, and the volume space velocity can be 0.5-3.0h -1 For example, 1, 2 or 2.5 hours -1 , the hydrogen to oil ratio may be 500-1500 V / V such as 800, 1000 or 1200 V / V.

[0018] In one embodiment, in step (1), the carrier of the hydrogenation catalyst loaded in the hydrogenation stabilization reactor is amorphous alumina or aluminum silicate; the metal in the active metal oxide supported on the catalyst carrier is selected from VIB and VIII groups; wherein the oxide component content of the VIB non-precious metal supported on the catalyst carrier is 5-30%, and the oxide component content of the VIII non-precious metal is 1-10%. The VIB group metal is Mo and / or W, and the VIII group metal is Co and / or Ni.

[0019] In one embodiment, in step (1), the hydrogenation stabilization reactor is a fixed bed hydrogenation reactor or an expanded bed reactor, preferably, an ebullating bed reactor with forced internal circulation.

[0020] In step (2) of the present invention, the coal indirect liquefaction crude oil is a synthetic crude oil obtained by a Fischer-Tropsch synthesis process, for example, it can be obtained by removing light components and solid residues from the product oil leaving the Fischer-Tropsch reactor, that is, no further hydrogenation reforming or hydrofining is required, and its distillation range can usually be in the range of 30 to 500°C. For details, please refer to the coal indirect liquefaction crude oil prepared by a Fischer-Tropsch synthesis method and system disclosed in CN101955788A.

[0021] In one embodiment, in step (2), the distillation temperature of the second distillation tower is 330-350°C, such as 340°C, wherein the fraction below the distillation temperature is taken as the second light distillate oil and enters the oil mixer.

[0022] In one embodiment, in step (3), the crude oil fraction from direct coal liquefaction (i.e., the first light distillate oil) and the crude oil fraction from indirect coal liquefaction (i.e., the second light distillate oil) are mixed in an oil product mixer in a ratio of 7:3-3:7, preferably 6:4-4:6, such as 5:5, to ensure the quality of the prepared diesel.

[0023] In one embodiment, in step (3), the reaction temperature of the hydrotreating reactor is 280-400°C, preferably 280-320°C, the reaction pressure is 8.0-20.0 MPa, preferably 8.0-1.5 MPa; the volume space velocity is 0.5-4.0 h -1 , preferably 0.5-2.0h -1 ; Hydrogen to oil ratio 500-1500V / V, preferably 500-1000V / V.

[0024] In one embodiment, in step (3), the carrier of the hydrotreating catalyst loaded in the hydrotreating reactor is amorphous alumina or aluminum silicate, and the metal in the active metal oxide supported on the catalyst carrier is selected from VIB and VIII groups; wherein the oxide component content of the VIB non-precious metal supported on the catalyst carrier is 0.5-30%, and the oxide component content of the VIII non-precious metal is 1-20%; the VIB group metal is Mo and / or W, and the VIII group metal is Co and / or Ni.

[0025] In a preferred embodiment, the active metal oxides supported by the carrier of the hydrorefining catalyst are MoO3, WO3 and NiO, wherein the content of the active metal oxide component is 8% to 25%, such as 9%, 12%, 15%, 18% or 20%, based on the total amount of the hydrorefining catalyst, wherein the content of the MoO3 is 8-20%, such as 10%, 15% or 18%, the content of the NiO is 1-6%, such as 1%, 3% or 5%, and the content of the WO3 is 0-10%; it is understood in the art that when the content is 0, it means that the component is not contained. The preparation of the supported hydrorefining catalyst is well known in the art. For example, in the present invention, taking the alumina carrier as an example, the supported catalyst is prepared by an impregnation method, and specific reference can be made to CN85104438A.

[0026] Preferably, in step (3), the hydrotreating reactor is a fixed bed reactor.

[0027] In one embodiment, in step (4), the distillation temperature during distillation is 160-170°C, such as 165°C, and the distillate oil above the distillation temperature is diesel, and the distillate oil below the distillation temperature is naphtha.

[0028] In the present invention, unless otherwise specified, the percentages involved are percentages by mass.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] 1. The characteristics of crude oil fractions from direct coal liquefaction are high sulfur and nitrogen content, high cyclic hydrocarbon and aromatic hydrocarbon content, low chain hydrocarbon content, but high density. Crude oil fractions from indirect coal liquefaction have low density, high chain hydrocarbon content, almost no sulfur, nitrogen and aromatic hydrocarbons, but high oxygen content and some olefins. Mixing crude oil from direct coal liquefaction with crude oil from indirect coal liquefaction balances the hydrocarbon composition of the raw materials, dilutes the content of heteroatoms, and has moderate density, thereby achieving complementary advantages and disadvantages of the two raw materials and reducing the difficulty of subsequent processing.

[0031] 2. In the original coal direct liquefaction process, the coal direct liquefaction crude oil is hydrogenated and stabilized before cutting, the heavy component is circulated to the coal direct liquefaction unit as a solvent, and the light component enters the hydrogenation and upgrading unit for hydrogenation and refining treatment. Therefore, the role of the hydrogenation and stabilization unit is ① to provide qualified solvent oil for the coal direct liquefaction unit. ② to provide stable raw materials for the downstream hydrogenation and upgrading device. In the hydrogenation and stabilization reaction process, the main reactions are partial saturation and removal of heteroatoms of aromatic hydrocarbons. If the hydrogenation is oversaturated, the content of saturated hydrocarbons in the circulating solvent will increase excessively. According to the principle of similar compatibility, the swelling capacity of the solvent for coal will be greatly reduced; if the hydrogenation depth is insufficient, the heteroatom content of the produced hydrogenation and upgrading raw materials will be high, and the upgrading catalyst will be easily poisoned. Therefore, in the present invention, the coal direct liquefaction crude oil is directly cut, the light component is directly mixed with the coal indirect liquefaction and then hydrogenated, and the heavy component is hydrogenated and stabilized by the solvent alone, so as to ensure the moderate hydrogenation of the solvent, so that the coal solubility and hydrogen supply capacity of the solvent are further improved, thereby improving the efficiency of coal direct liquefaction.

[0032] 3. The crude oil fraction from direct coal liquefaction and the crude oil fraction from indirect coal liquefaction can be processed together. Qualified diesel can be produced by hydrogenation refining, which greatly shortens the process flow and eases the process conditions.

[0033] 4. Due to the shortening of the process flow and the relaxation of process conditions, the products obtained by the combined processing have not undergone a deep degree of hydrogenation and retain more lubricating substances of the raw oil itself while meeting the national standard indicators. Therefore, the lubricity of the product is better. Compared with coal direct liquefaction diesel and coal indirect liquefaction diesel, the products of this process do not need to add or add less anti-wear agents, thereby reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The present invention is an implementation method of a diesel preparation system. DETAILED DESCRIPTION

[0035] The following is combined with Figure 1 The method provided by the present invention is further described, but the present invention is not limited thereby.

[0036] like Figure 1 As shown, the diesel preparation of the present invention includes the following process:

[0037] (1) The coal-oil slurry prepared by dissolving coal in a solvent is passed through a direct liquefaction reactor 11 to generate coal direct liquefaction crude oil, which enters a first distillation tower 12 for separation of the coal direct liquefaction crude oil. The heavy distillate oil is used as a solvent raw material and enters a solvent hydrogenation stabilization device 13 for solvent hydrogenation to generate a qualified solvent for recycling; the obtained first light distillate oil enters an oil product mixer 3.

[0038] (2) The coal gasification synthesis gas is synthesized into coal indirect liquefaction crude oil through the Fischer-Tropsch synthesis reactor 21, and enters the second distillation tower 22 for coal indirect liquefaction crude oil separation, and the second light distillate oil enters the oil product mixer 3.

[0039] (3) The mixed oil mixed in a certain proportion in the oil mixer 3 enters the hydrotreating reactor 4 for hydrogenation.

[0040] (4) Separating the hydrogenated product obtained in (3) to obtain naphtha and diesel; specifically, separating the hydrogenated refined product into hot high-fraction gas at the top and hot high-fraction oil at the bottom through a hot high-pressure separator 5; injecting deionized water (to prevent ammonium salt from clogging the pipeline) into the hot high-fraction gas at the top and then entering a cold high-pressure separator 6 to separate cold high-fraction oil and cold high-fraction gas, the cold high-fraction gas is discharged after metering, and the water separated by the cold high-pressure separator is discharged into a waste water tank; the hot high-fraction oil at the bottom of the hot high-pressure separator 5 enters a hot low-pressure separator 7 to separate hot low-pressure gas at the top and hot low-fraction oil at the bottom; the hot low-fraction gas at the top enters a cold low-pressure separator 8, the cold low-pressure separator 8 separates cold low-fraction gas at the top and cold low-fraction oil at the bottom, and the cold low-fraction gas is metered and discharged.

[0041] (5) The oil separated from the cold high-pressure separator 6, the hot high-pressure separator 7 and the hot low-pressure separator 8 are mixed and sent to the third separation tower 9 for cutting and separation, and naphtha and diesel are obtained after separation.

[0042] The hydrogenation part in the above treatment process consists of a hydrogenation stabilization reactor and a hydrogenation refining reactor. The purpose of the hydrogenation stabilization section is to process the solvent, improve the solvent's hydrogen supply performance and ensure the solvent's ability to dissolve coal. The purpose of the hydrogenation refining section is to remove sulfur, nitrogen, oxygen and other heteroatoms and saturated aromatics in the crude coal liquefaction oil to produce qualified diesel.

[0043] The beneficial effects of the present invention will be further described below in conjunction with specific embodiments.

[0044] According to the test process of the present invention, after coal is dissolved in a solvent and mixed with hydrogen, it enters a liquefaction device to undergo a direct coal liquefaction reaction, and the obtained direct liquefied crude oil is fractionated, and the heavy fraction oil greater than 300°C is subjected to a hydrogenation stabilization reaction to generate a qualified solvent for circulation to the coal liquefaction part. Synthesis gas enters a Fischer-Tropsch reactor for a Fischer-Tropsch synthesis reaction, and the obtained indirect liquefied crude oil is fractionated. The light oil fraction section less than 320°C and the light oil fraction section less than 300°C fractionated from the coal direct liquefaction unit are mixed in a certain proportion and hydrogenated into a hydrofining reactor, and a hydrofining reaction occurs to remove heteroatoms and saturated aromatics. The hydrofining distillate passes through a separation device system to separate naphtha fractions and diesel. The properties of the comparative examples and examples of crude oil are shown in Table 1 (the distillation range is determined by the ASTM D86 analysis method), the raw material ratios and process conditions of the examples are shown in Table 2, and the properties of the diesel product are shown in Table 3.

[0045] Comparative Example 1 in Table 2 and Table 3 uses coal direct liquefaction oil as raw material and the process is the same as Example 7; Comparative Example 2 uses coal indirect liquefaction oil as raw material and the process is the same as Example 8.

[0046] Comparative Example 3 in Table 3 is a coal direct liquefaction diesel prepared according to the process of the National Energy Group's million-ton coal direct liquefaction industrial demonstration unit (Ordos); Comparative Example 4 is a coal indirect liquefaction diesel prepared according to the process of the National Energy Group Ningxia Coal Industry's 4 million tons / year coal indirect liquefaction unit.

[0047] Table 1 Comparative Examples and Examples Raw Oil Properties

[0048]

[0049] Table 2 Process conditions of examples and comparative examples

[0050]

[0051]

[0052] Note: "0" in the table means that the component does not exist; the catalyst carrier is alumina.

[0053] Table 3 Diesel product properties

[0054]

[0055] As can be seen from Table 3, the combined processing of crude oil fractions from direct coal liquefaction and crude oil fractions from indirect coal liquefaction is simple and the process conditions are mild. The properties of the diesel product such as pour point, cetane number, sulfur and polycyclic aromatic hydrocarbon content all meet the main index requirements of GB17691-2016 diesel for vehicles, and the lubricity is better than that of existing diesel, and only a small amount of anti-wear agent is required to meet the standards.

[0056] Therefore, on the basis of the successful engineering implementation of existing direct coal liquefaction and indirect liquefaction, the oil quality improvement process units between the two are optimized and coupled. This can not only optimize the product structure, but also reduce the process complexity and improve the overall economic benefits of coal liquefaction technology, thereby providing useful exploration for the larger-scale industrial implementation of coal liquefaction technology.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing diesel, the method comprising the following steps: (1) Coal is dissolved in a solvent to prepare an oil-coal slurry, which is reacted with hydrogen to directly liquefy the coal. The generated coal direct liquefaction crude oil is separated in a first fractionation tower to obtain a first light distillate oil and a heavy distillate oil; the first light distillate oil enters an oil product mixer; the heavy distillate oil is used as a solvent raw material and subjected to solvent hydrogenation stabilization in a hydrogenation stabilization reactor; wherein the fractionation temperature of the first fractionation tower is 290-300°C, the fraction below the fractionation temperature is taken as the first light distillate oil, and the fraction above the fractionation temperature is taken as the heavy distillate oil; (2) The coal gasification synthesis gas is subjected to Fischer-Tropsch synthesis reaction, and the synthesized coal indirect liquefaction crude oil is separated by a second distillation tower to obtain a second light distillate oil and wax, and the second light distillate oil enters the oil product mixer; wherein, the distillation temperature of the second distillation tower is 330-350°C, and the fraction below the distillation temperature is taken as the second light distillate oil and enters the oil product mixer; (3) after mixing the first light distillate oil and the second light distillate oil in the oil product mixer, subjecting the obtained mixed oil to a hydrotreating reaction in a hydrotreating reactor; wherein the mass mixing ratio of the first light distillate oil and the second light distillate oil in the oil product mixer is 7:3-3:7; (4) The hydrogenation product obtained in step (3) is fractionated to obtain a diesel product.

2. The method according to claim 1, characterized in that In step (1), the reaction temperature of the hydrogenation stabilization reactor is 300-400°C, the reaction pressure is 12.0-20.0 MPa, the volume space velocity is 0.5-3.0 h-1, and the hydrogen-to-oil ratio is 500-1500 V / V.

3. The method according to claim 1, characterized in that In step (1), the carrier of the hydrogenation catalyst loaded in the hydrogenation stabilization reactor is amorphous alumina or aluminum silicate, and the active metals loaded on the catalyst carrier are VIB and VIII groups; wherein, based on the total amount of the hydrogenation catalyst, the mass content of the VIB non-precious metal component loaded on the catalyst carrier is 5-30%, and the mass content of the VIII non-precious metal component is 1-10%; the VIB group metal is Mo and / or W, and the VIII group metal is Co and / or Ni.

4. The method according to claim 1, characterized in that: In step (1), the hydrogenation stabilization reactor is a fixed bed hydrogenation reactor or an expanded bed reactor.

5. The method according to claim 1, characterized in that: In step (1), the hydrogenation stabilization reactor is an ebullating bed reactor using forced internal circulation.

6. The method according to claim 1, characterized in that In step (3), the reaction temperature of the hydrotreating reactor is 280-380°C; the reaction pressure is 8.0-20.0 MPa; the volume space velocity is 0.5-4.0 h-1; and the hydrogen-to-oil ratio is 500-1500 V / V.

7. The method according to claim 5, characterized in that In step (3), the reaction temperature of the hydrotreating reactor is 280-320°C; the reaction pressure is 8.0-1.5 MPa; the volume space velocity is 0.5-2.0 h-1; and the hydrogen-to-oil ratio is 500-800 V / V.

8. The method according to claim 1, characterized in that In step (3), the carrier of the hydrotreating catalyst loaded in the hydrotreating reactor is amorphous alumina or aluminum silicate, and the active metals loaded on the catalyst carrier are VIB and VIII groups; wherein, based on the total amount of the hydrotreating catalyst, the mass content of the VIB non-precious metal component loaded on the catalyst carrier is 0.5-30%, and the mass content of the VIII non-precious metal component is 1-20%; the VIB group metal is Mo and / or W, and the VIII group metal is Co and / or Ni.

9. The method according to claim 8, characterized in that In step (3), the hydrotreating reactor is a fixed bed reactor.

10. The method according to claim 1, characterized in that In step (4), the fractionation temperature during fractionation is 160-170°C, the distillate oil above the distillation temperature is taken as diesel, and the distillate oil below the distillation temperature is taken as naphtha.

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